Nickel Hydroxide Particle Size and Nickel Layer Thickness in NiMH Batteries
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Solution Overview
Problem
Nickel-metal hydride batteries face issues with low current collecting properties and shortened lifespan due to the conversion of small-diameter nickel hydroxide particles to γ-type nickel oxyhydroxide during charge and discharge cycles, leading to expansion and electrolyte depletion.
Innovation Solution
A battery design with a positive electrode substrate having a three-dimensional network structure and nickel hydroxide particles, where the content of particles with a diameter of 5 μm or less is limited to 15 wt%, and the nickel layers on the substrate are configured such that the average thickness of the middle nickel layer is 60% or more of the thicker front-surface or back-surface nickel layers, ensuring improved current collection and reduced γ-type nickel oxyhydroxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If small-diameter nickel hydroxide particles (5 μm or less) are filled in relatively large amounts (20 wt % or more) to improve current collecting property, then the current collecting property is enhanced, but the particles convert to γ-type nickel oxyhydroxide during charge and discharge cycles, causing expansion and electrolyte depletion which shortens battery life
Solution Approach 1:
The patent changes the particle size parameter of nickel hydroxide, specifically using particles with a diameter of more than 5 μm (contrary to the conventional small particles of 5 μm or less). This parameter change prevents the conversion to γ-type nickel oxyhydroxide while maintaining good current collecting properties, thus resolving the contradiction between improving current collection and extending battery life
Solution Approach 2:
The patent applies local quality by creating a specific particle size distribution where the majority of nickel hydroxide particles have a diameter of more than 5 μm, while allowing a controlled small amount of finer particles. This localized differentiation in particle size throughout the electrode structure optimizes both current collection and structural stability during cycling
2Ease of manufacture
If the middle nickel layer is made thinner (as occurs in conventional electrolytic nickel plating) to reduce material usage, then manufacturing cost is reduced, but the current collecting property in the middle portion of the positive electrode substrate deteriorates
Solution Approach 1:
The patent applies local quality by creating a non-uniform nickel layer thickness distribution where the middle nickel layer is thicker than the front-surface and back-surface nickel layers. Specifically, the middle nickel layer thickness is set to 0.7 times or more of the front-surface nickel layer thickness. This localized thickening in the middle portion compensates for the naturally thinner middle layer formed during electrolytic plating, ensuring adequate current collection throughout the electrode while maintaining manufacturing efficiency
Solution Approach 2:
The patent introduces asymmetry in the nickel layer structure by deliberately making the middle nickel layer thicker relative to the surface layers, creating an inverted thickness profile compared to conventional uniform or surface-thick designs. This asymmetric configuration optimizes current distribution in the middle portion of the electrode where it is naturally thinner during standard plating processes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the battery's current collecting properties and extends its lifespan by minimizing the conversion of nickel hydroxide particles to γ-type nickel oxyhydroxide, thereby reducing internal resistance and maintaining electrolyte levels.
Implementation Method 1
the nickel hydroxide will change to inert γ-type nickel oxyhydroxide in association with repeated charge and discharge cycles
Implementation Method 2
immersed in an electrolytic nickel plating solution in which a predetermined mount of current is supplied to a front-surface-side electrode placed facing the front surface of the foamed urethane substrate
Data Source
AI summary
A battery is adapted such that a nickel hydroxide particle group constituted of a number of nickel hydroxide particles filled in a void part of a positive electrode substrate contains, at a ratio of 15 wt % or less, small-diameter nickel hydroxide particles each having a particle diameter of 5 μm or less. The positive electrode substrate is configured such that a front-surface-side nickel layer and a back-surface-side nickel layer are made larger in thickness than a middle nickel layer, and an average thickness B of either the front-surface-side nickel layer or the back-surface-side nickel layer, which is thicker one, and an average thickness C of the middle nickel layer satisfy a relation of C/B≧0.6.